1. Field of Invention
The invention relates to a zoom lens and, in particular, to a wide-angle (greater than 70 degrees) zoom lens for digital cameras that can reach more than 10xc3x97 zoom ratio.
2. Related Art
In recent years, we observe the trend of compact and light lenses on many digital image capture devices, such as digital cameras and digital video camcorder(DVC""s). The advantages of these lenses attribute to the minimization of the length of the lens set, the front lens element and the simplification of the lens set.
To achieve the above objective, the focus mechanism is moved from the conventional front element or the first element to the least lens sets. This introduces the so-called back-element focusing. The back-element focusing design is superior to those in the prior art. The size of the first clement is greatly reduced for the convenience of minimization of lenses. This enables the ultra-short focusing for macro lenses. Because of the minimization of the lens, the driving force to push the lens by the image capture device is reduced. Moreover, the focusing can be quickly achieved using the current driving mechanism.
On the other hand, aberrations occurred to the back-element focusing system are not easy to control, resulting in difficult control of the image quality. Increasing the zooming range also deteriorates the image quality. Restricted by these limits, the image quality obtained using the lenses in the prior art cannot be improved. The effect of accessory wide-angle lenses on cameras is very limited and may have large distortions. They are also very inconvenient for the users to carry.
The most important issue is the optical design restriction. Compactness and lightness are never achieved in the DVC""s. The usual viewing angle is about 60 degrees. We do not find any patent or literature that addresses the question of having a viewing effect with angles wider than 64 degrees.
In view of the foregoing, the invention discloses a 10xc3x97 zoom ratio wide-angle zoom lens. A primary objective of it is to achieve both wide angles (up to 70 degrees) and a 10xc3x97 zoom ratio magnification power under the premises of keeping good image quality and satisfying the requirements of compactness and lightness. The invention contains a first lens set with a positive dioptre, a second lens set with a negative dioptre, a third lens set with a positive dioptre and a fourth lens set with a positive dioptre. The second lens set further contains two lenses with negative dioptres and one lens with a positive dioptre. The lens with a positive dioptre has a non-spherical surface on the object side. The lens with a negative dioptre closer to the lens with a positive dioptre is cemented to the positive-dioptre lens. The fourth lens set contains a lens with a negative dioptre and two non-spherical surfaces. The wide-angle zoom lens moves the second lens set and the fourth lens set along its optical axis to adjust its zoom and moves the fourth lens set to focus.
The invention has the design concept of compactness and lightness. Along with the non-spherical lens technology, a wide-angle optical design is achieved and suitable for current market demands.